Link goes to instructions on how to get the game, which I've copied below.
1. Go to www.onlive.co.uk, and create an OnLive account (UK)
2. Download, Install and sign into the OnLive Application
3. Run the application. Once in the OnLive game service:
Select Zeno Clash (it is a featured game)
Select “Get Game”
Select “Full PlayPass” and click “Next”
Enter in NDFREEUK in code box, apply it, select “Purchase”
Start Playing! (Your game will be in your “My Games” tab for now on)
There will be another free game next weekend, and if they get 1000 shares (yup, shares only, likes do NOT count) of this: www.facebook.com/photo.php?fbid=10151121797375091 then they'll give away two games instead.
For those of you who don't know, OnLive is a cloud gaming service. You don't download and install the game - instead it's streamed to your computer when you play it. You'll need a fast internet connection and it uses up data (worth remembering if you have a data allowance), but you are able to play games that your computer is too slow to run otherwise. I think OnLive uses about 2 gig an hour.
This is the first of three weekends of giving away a free game, and yes, you get to keep it permanently. Offer ends August 12th at 11:59 PDT, so I guess that's 20.00 for us Brits.